Reference
Santos, D., Monteiro, C., Matias, C., Silva, A. (2011). Magnesium intake is associated with strength performance in elite basketball, handball and volleyball players. Magnes Res. doi: 10.1684/mrh.2011.0290
Introduction: Magnesium is considered a trace mineral required in small to moderate doses to optimize health and athletic performance. Increasing amounts of data support magnesium’s role in cardiovascular health and muscle strength. Plasma magnesium levels have been shown to have an impact on grip strength and muscle power. Low levels of magnesium are associated with increased damage to muscle cells. A number of mechanisms have been proposed to explain the increase in muscle damage including increased reactive oxygen species, reduced ATP formation, lipid and protein damage, and decreased calcium homeostasis. Studies in athletes have demonstrated magnesium intake to be below the Recommended Daily Allowance (RDA)(400 mg/day). This appears to be associated with increasing consumptions of processed foods, which typically has minimal to no magnesium. To date, little research has examined the relationship between magnesium and strength and performance in the athletic population. Therefore, the purpose of this research study was to establish a relationship between baseline, preseason magnesium intake and strength performance profiles of elite male volleyball, basketball, and handball players.
The authors’ introduction was relatively brief, I feel they could have elaborated more on the possible performance benefits of magnesium. Through a brief literature review I have seen possible mechanisms such as improved neural performance. The authors did touch on why low magnesium levels may impair performance. Overall, I feel this section could be improved upon.
Purpose: The purpose of this study was to establish baseline levels of magnesium levels in elite male athletes and examine the possible relationship between magnesium levels and muscle strength.
Subject Description: The study included 26 male elite athletes from basketball (n=11), handball (n=7), and volleyball (n=8). The physical characteristics of the athletes were provided in a table. The mean age of the athletes was 20.1±4.9 years. The mean weight was 81.9±8.9 kg. The mean height was 190.2±7.9 cm. The mean BMI, fat free mass (FFM), fat mass (FM), and % FM were as follows: 22.6±2.1 kg/m2, 69.36±6.89 kg, 11.87±3.30 kg, 14.47±2.92 %.
Again, this was relatively all that was included by the authors. There was no mention of how the subjects were recruited. In addition, definitions such as what is considered an “elite” athlete were not provided. This leaves the reader wondering the experience levels of the athletes in their respective sports. Are these collegiate level athletes or are they playing professionally in their respective sports. The age of the subjects indicates they are relatively young (20). The physical characteristics were easy to read in a simple table.
Methods and Procedures: Body Composition (FFM, FM, %FM) were assessed using dual energy X-ray absorptiometry (DEXA). Strength tests were performed in the afternoon after a standardized warm-up. Maximal isometric force for the lumbar-thoracic column were assessed using F110, F130, and F120 David devices at 15◦. Isometric hand grip strength was determined via handgrip dynamometer (Jamar). Squat jump (SJ) and Countermovement jump Abalakov (CMJA) were assessed using custom software (BioPlux System). Isokinetic peak torque at 60◦ (PT60) and 180◦·s-1 (PT180) were assessed using an isokinetic dynamometer (Biodex). Twenty four hour diet records were kept for a 7-day period. Subjects were educated on portion sizes, supplements, and other areas to ensure accuracy. After the 7-day period athletes were interviewed by a nutritionist to clarify any discrepancies in the diet record. Diets were then analyzed by the software package Food Process.
The protocol for this study was not complex and therefore did not require enormous amounts of details. Despite this, the authors could have done a better job at explaining the testing details. For instance, the angle of arm bend during hand grip testing was not provided. The number of trials of each was not recorded. Did the authors use highest squat jump or average of a number of trials? These are simple questions that would have been eliminated had the authors gone into more details about the testing procedures. The use of a diet record may not be the most accurate method of tracking food intake. It would have been better to have the athletes eat their normal food under some sort of supervision or even using technology to ensure everything was tracked.
Statistical Analysis: Data was analyzed using SPSS (19.0). Statistical significance was set at 0.1 and linear regression was used to analyze the relationship between magnesium intake and strength.
Results: Magnesium intake was found to be significantly lower than RDA (244.7±78.8 mg) (p<0.001). Additionally, the calcium to magnesium ratio was found to be higher than the recommended ration of 2:1 (3.96±1.21). Regression analysis indicated magnesium intake was associated with flexion (R2=0.193, p=0.028), rotation (R20.357, p=0.055), handgrip (R2 =0.111, p=0.027), SJ (R2=0.254, p=0.070), CMJA (R2 = 0.290, p=0.075)and isokinetic testing (PT60/180) (PT60 Extension R2= 0.214, p=0.016) (PT60 flexion,R2= 0.411, p=0.002)(PT 180 Extension R2= 0.431 , p<0.001)(PT 180 Flexion, R2= 0.589, p <0.001 ).
The results section was reported adequately. The use of a table and regression graphs made the results easy to interrupt. Despite the short-comings in the intro and methods section, it does appear magnesium levels are associated with performance. If the results had been less unanimous (significance in every test except trunk extension), the lack of details in the methods would make these results more difficult to interrupt. For example, without feeling 100% certain the diets were tracked accurately, the reader may question if the athletes really were magnesium deficient. Also, better evaluation of the diet would allow for the scientists to interrupt if other micronutrients may be responsible, and the lack of magnesium is simply a casual association.
Discussion: This study reveals that elite male athletes consume less than the RDA recommended intake of 400 mg of magnesium. In addition, the ratio of calcium to magnesium was found to be higher than the recommended ratio of 2:1. This higher ratio may reduce magnesium uptake and compromise cellular availability. The reduction in strength observed in this study may explain magnesium’s role in energy metabolism, transmembrane transport, and muscle contraction and relaxation. This study demonstrated a direct association between magnesium intake and muscular performance. Magnesium intake and performance was demonstrated even after correcting for differences in energy intake and appears to be independent of energy intake. These results suggest the importance of magnesium’s role in muscle performance while also demonstrating improved dietary guidelines are needed to ensure adequate magnesium intake in athletic populations.
My Thoughts: The authors failed to mention any limitations in their study. The limitations include a small sample, no control group, limited methods, and a failure to perform a full nutritional panel. I also felt the author’s over-reached in their discussion. I am not sure there was a direct association between magnesium intake and strength. I feel this was more of a causal relationship at this time. For instance, it is plausible the athletes also lacked other micronutrients such as vitamin D. Without a full nutritional panel it is hard to tell whether it is truly magnesium or if there is another variable which could explain deficits in strength. Overall, this study left a lot on table in regards to details, methods, and overall investigation. I would like to see a follow-up study in which magnesium was supplemented, and then strength measures re-tested. This would help paint a clearer picture in regards to magnesium’s role in muscle performance.
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